December 15, 2012

A huge, billowing pair of gas and dust clouds are captured in this stunning NASA Hubble Space Telescope image of the supermassive star Eta Carinae.

Using a combination of image processing techniques (dithering, subsampling and deconvolution), astronomers created one of the highest resolution images of an extended object ever produced by the Hubble Space Telescope. The resulting picture reveals astonishing detail.

Even though Eta Carinae is more than 8,000 light-years away, structures only 10 billion miles across (about the diameter of our solar system) can be distinguished. Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity.

Eta Carinae was observed by Hubble in September 1995 with the Wide Field Planetary Camera 2 (WFPC2). Images taken through red and near-ultraviolet filters were subsequently combined to produce the color image shown. A sequence of eight exposures was necessary to cover the object's huge dynamic range: the outer ejecta blobs are 100,000 times fainter than the brilliant central star.

Eta Carinae was the site of a giant outburst about 150 years ago, when it became one of the brightest stars in the southern sky. Though the star released as much visible light as a supernova explosion, it survived the outburst. Somehow, the explosion produced two polar lobes and a large thin equatorial disk, all moving outward at about 1.5 million miles per hour.

The new observation shows that excess violet light escapes along the equatorial plane between the bipolar lobes. Apparently there is relatively little dusty debris between the lobes down by the star; most of the blue light is able to escape. The lobes, on the other hand, contain large amounts of dust which preferentially absorb blue light, causing the lobes to appear reddish.

Estimated to be 100 times more massive than our Sun, Eta Carinae may be one of the most massive stars in our Galaxy. It radiates about five million times more power than our Sun. The star remains one of the great mysteries of stellar astronomy, and the new Hubble images raise further puzzles. Eventually, this star's outburst may provide unique clues to other, more modest stellar bipolar explosions and to hydrodynamic flows from stars in general.

After the Sun sets on a summer evening and the sky fades to black, you may be lucky enough to see thin, wavy clouds illuminating the night, such as these seen over Billund, Denmark, on July 15, 2010. Noctilucent or polar mesospheric clouds, form at very high altitudes—between 80 and 85 kilometers (50–53 miles)—which positions them to reflect light long after the Sun has dropped below the horizon. These “night-shining” clouds are rare—rare enough that Matthew DeLand, who has been studying them for 11 years, has only seen them once in person. But the chances of seeing these elusive clouds are increasing.

DeLand, an atmospheric scientist with Science Systems and Applications Inc. and NASA's Goddard Space Flight Center, has found that polar mesospheric clouds are forming more frequently and becoming brighter. He has been observing the clouds in data from Solar Backscatter Ultraviolet instruments that have been flown on satellites since 1978. The graph above shows how the brightness of the clouds has changed in the Northern Hemisphere. For reasons no one fully understands, the brightness wiggles up and down in step with solar activity, with fewer clouds forming when the Sun is most active. The biggest variability is in the far north. Underlying the changes caused by the Sun, however, is a trend toward brighter clouds. The upward trend in brightness, says DeLand, reveals subtle changes in the atmosphere that may be linked to greenhouse gases.

Polar mesospheric clouds are extremely sensitive to changes in atmospheric water vapor and temperature. The clouds form only when temperatures drop below -130 degrees Celsius (-200 Fahrenheit), when the scant amount of water high in the atmosphere freezes into ice clouds. This happens most often in far northern and southern latitudes (above 50 degrees) in the summer when, counter-intuitively, the mesosphere is coldest.

Changes in temperature or humidity in the mesosphere make the clouds brighter and more frequent. Colder temperatures allow more water to freeze, while an increase in water vapor allows more ice clouds to form. Increased water vapor also leads to the formation of larger ice particles that reflect more light.

The fact that polar mesospheric clouds are getting brighter suggests that the mesosphere is getting colder and more humid, says DeLand. Increasing greenhouse gases in the atmosphere could account for both phenomena. In the mesosphere, carbon dioxide radiates heat into space, causing cooling. More methane, on the other hand, puts more water vapor into the atmosphere because sunlight breaks methane into water molecules at high altitudes.

So far, it’s not clear which factor—water vapor or cooling—is causing polar mesospheric clouds to change. It’s likely that both are contributing, says DeLand, but the question is the focus of current research.

December 14, 2012

This spectacular image of sunset on the Indian Ocean was taken by astronauts aboard the International Space Station (ISS). The image presents an edge-on, or limb view, of the Earth’s atmosphere as seen from orbit. The Earth’s curvature is visible along the horizon line, or limb, that extends across the image from center left to lower right. Above the darkened surface of the Earth, a brilliant sequence of colors roughly denotes several layers of the atmosphere.

Deep oranges and yellows appear in the troposphere, which extends from the Earth’s surface to 6–20 km high. This layer contains over 80 percent of the mass of the atmosphere and almost all of the water vapor, clouds, and precipitation. Several dark cloud layers are visible within this layer. Variations in the colors are due mainly to varying concentrations of either clouds or aerosols (airborne particles or droplets).

The pink to white region above the clouds appears to be the lower stratosphere; this atmospheric layer generally has few or no clouds, and it extends up to approximately 50 kilometers above the Earth’s surface. Above the stratosphere, blue layers likely mark the transition between the middle and upper atmosphere as it gradually fades into the blackness of outer space.

The ISS was located over the southern Indian Ocean when this picture was taken, with the astronaut looking towards the west. Astronauts aboard the ISS see 16 sunrises and sunsets per day due to their high orbital velocity (greater than 28,000 km per hour). The multiple chances for photography are fortunate because at that speed, each sunrise or sunset only lasts a few seconds!

On September 26, 2011, a large solar Coronal Mass Ejection smacked into planet Earth's magnetosphere producing a severe geomagnetic storm and wide spread auroras. Captured here near local midnight from Kvaløya island outside Tromsø in northern Norway, the intense auroral glow was framed by parting rain clouds. Tinted orange, the clouds are also in silhouette as the tops of the colorful shimmering curtains of northern lights extend well over 100 kilometers above the ground. Though the auroral rays are parallel, perspective makes them appear to radiate from a vanishing point at the zenith. Near the bottom of the scene, an even more distant Pleiades star cluster and bright planet Jupiter shine on this cloudy northern night.

December 11, 2012

In this detailed view from NASA's Hubble Space Telescope, the so-called Cat's Eye Nebula looks like the penetrating eye of the disembodied sorcerer Sauron from the film adaptation of "The Lord of the Rings."

The nebula, formally cataloged NGC 6543, is every bit as inscrutable as the J.R.R. Tolkien phantom character. Though the Cat's Eye Nebula was one of the first planetary nebulae to be discovered, it is one of the most complex such nebulae seen in space. A planetary nebula forms when Sun-like stars gently eject their outer gaseous layers that form bright nebulae with amazing and confounding shapes.

As if the Cat's Eye itself isn't spectacular enough, this new image taken with Hubble's Advanced Camera for Surveys (ACS) reveals the full beauty of a bull's eye pattern of eleven or even more concentric rings, or shells, around the Cat's Eye. Each 'ring' is actually the edge of a spherical bubble seen projected onto the sky — that's why it appears bright along its outer edge.

Observations suggest the star ejected its mass in a series of pulses at 1,500-year intervals. These convulsions created dust shells, each of which contain as much mass as all of the planets in our solar system combined (still only one percent of the Sun's mass). These concentric shells make a layered, onion-skin structure around the dying star. The view from Hubble is like seeing an onion cut in half, where each skin layer is discernible.

Until recently, it was thought that such shells around planetary nebulae were a rare phenomenon. However, Romano Corradi (Isaac Newton Group of Telescopes, Spain) and collaborators, in a paper published in the European journal Astronomy and Astrophysics in April 2004, have instead shown that the formation of these rings is likely to be the rule rather than the exception.

The bull's-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would repeat every 1,500 years. Several explanations have been proposed, including cycles of magnetic activity somewhat similar to our own Sun's sunspot cycle, the action of companion stars orbiting around the dying star, and stellar pulsations. Another school of thought is that the material is ejected smoothly from the star, and the rings are created later on due to formation of waves in the outflowing material. It will take further observations and more theoretical studies to decide between these and other possible explanations.

Approximately 1,000 years ago the pattern of mass loss suddenly changed, and the Cat's Eye Nebula started forming inside the dusty shells. It has been expanding ever since, as discernible in comparing Hubble images taken in 1994, 1997, 2000, and 2002. The puzzle is what caused this dramatic change? Many aspects of the process that leads a star to lose its gaseous envelope are still poorly known, and the study of planetary nebulae is one of the few ways to recover information about these last few thousand years in the life of a Sun-like star.

NASA’s DC-8 flying laboratory passes Antarctica’s tallest peak, Mount Vinson, on October 22, 2012, during a flight over the continent to measure changes in the massive ice sheet and sea ice. The flight is part of NASA’s Operation IceBridge, a multi-year airborne campaign to monitor changes in Earth’s polar ice caps in both the Antarctic and Arctic. IceBridge science flights from Punta Arenas, Chile, began on October 12 and continue through early November. Mount Vinson is located in the Sentinel Range of the Ellsworth Mountains in Antarctica.